This invention lies in the field of fluid valves. More particularly it concerns the type of value known as the butterfly valve, which has a limited axial width, and is installed in a line by clamping between pipe flanges.
Still more particularly it is concerned with a type of butterfly valve in which the valve can be closed and sealed with minimum torque on the operating shaft, while providing a positive self energizing seal.
In the prior art butterfly valves have been designed with rotatable closure discs having ridged edges. However, in these valves, the plane of the disc is at an angle to the shaft. With this geometry it is impossible to provide a self energizing seal. Therefor, to provide a positive seal, it is necessary to make the disc considerably oversize, so as to penetrate a sufficient distance into the elastomeric seating surface to develop sufficient internal pressure to provide the necessary seal against the pressure of the fluid flowing through the valve.